Update exp to sql

Src/Asp.Net/SqlSugar/ExpressionsToSql/Common/ExpressionTool.cs

@@ -559,5 +559,21 @@ namespace SqlSugar
             }
             return false;
         }
+
+        internal static bool IsIsNullSubQuery(Expression it)
+        {
+            if (it is MethodCallExpression)
+            {
+                var method = (MethodCallExpression)it;
+                if (method.Method.Name == "IsNull")
+                {
+                    if (method.Arguments.Count==2&&IsSubQuery(method.Arguments[0])) 
+                    {
+                        return true;
+                    }
+                }
+            }
+            return false;
+        }
     }
 }

Src/Asp.Net/SqlSugar/ExpressionsToSql/ResolveItems/MethodCallExpressionResolve_Helper.cs

@@ -116,6 +116,22 @@ namespace SqlSugar
                     }
                 }
             }
+            else if (this.Context.IsSingle && args.Any(it => ExpressionTool.IsIsNullSubQuery(it)) )
+            {
+                var exp = base.BaseParameter?.BaseParameter?.BaseParameter?.CurrentExpression;
+                if (exp is LambdaExpression)
+                {
+                    SetShortName(exp);
+                }
+                else if (exp is UnaryExpression)
+                {
+                    exp = base.BaseParameter?.BaseParameter?.BaseParameter?.BaseParameter?.CurrentExpression;
+                    if (exp is LambdaExpression)
+                    {
+                        SetShortName(exp);
+                    }
+                }
+            }
             var isBinaryExpression = item is BinaryExpression || item is MethodCallExpression;
             var isConst = item is ConstantExpression;
             var isIIF = name == "IIF";